(a) Field of the Invention
The present invention relates to a cathode ray tube (CRT) and a method of manufacturing the same and, more particularly, to a CRT manufacturing method which removes one of the serious defects generated in the CRT manufacturing process, called a beam-guide hole clogging defect of a shadow mask and prevents deterioration of the electron emission deficiency of an electron gun and occurrence of a crack while reducing the number of the CRT processing steps.
(b) Description of the Related Art
Generally, CRTs are designed to reproduce the original picture image on a glass screen through receiving the picture image signals from the external and exciting phosphors coated on the screen with electron beams emitted from the electron gun in accordance with the signals.
FIG. 8 is a schematic cross sectional view of the generally well-known CRT. As shown in the figure, the CRT usually includes a panel 4 having a phosphor screen 2, a funnel 8 bonded together with the panel 4 in a vacuum-tight manner and mounting a deflection unit 6 thereon, and a neck 12 connected to the funnel 8 in the rear to accommodate an electron gun 10 therein.
The electron gun 10 is mounted on a stem 14 to receive current for emitting, focusing and accelerating thermal electrons from it. The stem 14 is fitted into the neck 12 in such a manner as to provide a vacuum-tight seal between them.
A conventional method of sealing the stem to the neck will be now described with reference to FIG. 7.
FIG. 7 is a cross sectional view of a neck 12 and stem S before performing a sealing operation. As shown in the figure, the sealing operation is performed in such a state that the stem S is deeply inserted into the inside of the neck 12. At this state, the lateral surface of the neck 12 adjacent to a flange of the stem S is heated using torches T till it is fused to thereby provide a seal together with the stem S, and the remaining end portion of the neck 12 is removed and waste-disposed.
However, when the end portion of the neck N is cut off or drops to be thereby broken to pieces, a fine glass powder is generated.
The glass powder wanders through the factory and intrudes into the inside of the CRT through the exhaust pipe externally attached to the stem or through the opening portion of the neck before the sealing operation so that it clogs beam-guide holes formed on the shadow mask. This causes a serious defect in the CRT processing, called a beam-guide hole clogging defect.
Furthermore, since the remaining end portion of the neck is cut off and waste-disposed after the sealing operation, a minus effect is resulted in the production costs.
In the meantime, another conventional method of sealing the stem to the neck is disclosed in a Japanese Patent No. 8-83582. In the method, the sealing operation is performed in such a state that the bottom end of the neck is positioned on the upper portion of the stem flange.
Meanwhile, in order to provide a vacuum-tight seal between the neck and stem at that state, the bottom end of the neck should uniformly contact the upper portion of the flange. However, such an uniform contact cannot be practically obtained because an error may be occurred in fixing the neck on a predetermined position. Moreover, the end portion of the neck as well as the upper portion of the flange may not be even.
Accordingly, there is always a gap between the bottom end of the neck and the upper portion of the flange due to their rough contact. And when the heating operation is performed onto the gapped contact side by the heating element such as a torch, the torch flame penetrates into the inside of the neck through the gap. As a result, the electrodes of the electron gun and the stem pins are oxidized so that the electron emission efficiency is deteriorated.
Furthermore, it is required that an additional step of moving the stem toward the neck should be added to provide a vacuum-tight seal between the stem and neck by removing the gap therebetween.
Moreover, since the end portion of the neck should be fused on the upper portion of the stem flange, the fused portion may contact protrusions of the stem pins, thereby causing a crack.